题目内容
The crawl frontier includes the seed URLs and all their hyperlinks.
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URLs from the frontier need visiting only once.
To prioritize its downloads means to determine the order according to their relative importance.
The heavy task of a Web crawler lies in the large volume of Web pages, their high rate of change and the difficulty to avoid retrieving duplicate content.
Endless combinations of HTTP GET (URL-based)parameters are useful for the crawler to get unique content.
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